We give an overview of the photometric calibration of the Short Wavelength Spectrometer (SWS) through the Performance Verification phase. The basic strategy for deriving absolute flux densities from detector output for the grating and Fabry-Perot sections of SWS is reviewed, and the results are demonstrated with 2.4 - 45 mu m spectra of representative standards gamma Dra, alpha Lyr, and gamma Cru. The effects of in-orbit changes in the relative spectral response function (RSRF) and ISO pointing are discussed. The systematic continuum flux level uncertainties (1 sigma) are within the pre-launch specification of 30%. Further improvements depend on characterization of the in-orbit RSRF improved performance of ISO pointing, and new data processing techniques.